The present invention relates, in general, to autosamplers for use with chemical separation and analysis methods which have means for identifying the separated components: gas chromatography, gas chromatography mass spectroscopy and high performance liquid chromatography, to name a few.
During the last eight years, a new concept for concentrating analytes for analysis has been developed. The most widely accepted generic term for this methodology is “Liquid Phase Microextraction or LPME”. The technique involves the use of 1–5 microliters of solvent to concentrate chemicals present in water, air or the head space atmosphere above a liquid or solid sample. After the chemicals are concentrated from the medium into the solvent, the liquid is injected into an appropriate chromatography instrument for separation and analysis, or directly analyzed if component separation is not necessary.
The applications of this technique are wide-ranging and growing. The method has been used to analyze pharmaceuticals and environmental contaminants in blood, organic environmental chemicals in water, and solvents and impurities in solids, to name a few examples.
LPME can be used with almost any analytical method, including GG, GC/MS, HPLC, Capillary Electrophoresis separation-analysis methods, or without separation techniques using FTIR, UV/VIS, NMR or MS. LPME and Microdrop Head Space Analysis (or MDHA) techniques allow dilute or even relatively concentrated samples in complex sample matrices to be concentrated into a small solvent volume for analysis.
The general procedure for LPME involves the following steps: 1) a solvent is drawn into a sampling device, commonly a syringe or adapted syringe-like device, 2) a microdrop of the solvent is then forced out of the syringe onto the tip of the syringe needle and into the medium to be sampled, 3) the chemicals of interest are partitioned into the solvent over a period of a few minutes, and 4) the solvent microdrop is withdrawn into the syringe and the sample concentrate then analyzed.
The solvent microdrop can be exposed directly to the sample medium, or it can be encased in a polymeric hollow fiber or film which is immersed in the medium and into which the sample can also partition into. The latter method protects the microdrop from being removed from the needle tip during the sampling period. As with all sampling techniques, in order to obtain good reproducible analytical results with this method, the timing and precision of each of the above steps must be reproducible. To this point, this method has suffered from the lack of automated reproduction of these manual steps.
A number of manufacturers sell autosamplers which can perform multiple injections in gas chromatography or liquid chromatography of varying sample volumes. However, such autosamplers and automation methods have been employed only with the insertion of the syringe into the sample and the extraction of a portion of the sample into the syringe. Heretofore, there has not been an automated method for liquid phase microextraction thereby requiring the manual ejecting of a microdrop of a solvent out of the syringe and onto the tip of the syringe needle in the head space above the sample or into the medium to be sampled. This is a tedious task when numerous samples must be analyzed and requires precise and continued plunger control to maintain the microdrop on the tip of the plunger for the sample period. This is a difficult manual task, especially for numerous samples.
Thus, it would be desirable to provide automated reproduction of liquid phase microextraction methodology or process steps. It would also be desirable to provide an automated method for liquid phase microextraction which can be easily implemented in existing autosampling equipment.